//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Windows;
using Microsoft.Practices.Prism.Regions.Behaviors;
using Windows.UI.Xaml;

namespace Microsoft.Practices.Prism.Regions
{
	/// <summary>
	/// Class that holds methods to Set and Get the RegionContext from a DependencyObject. 
	/// 
	/// RegionContext allows sharing of contextual information between the view that's hosting a <see cref="IRegion"/>
	/// and any views that are inside the Region. 
	/// </summary>
	public static class RegionContext
	{
		private static readonly DependencyProperty ObservableRegionContextProperty =
			DependencyProperty.RegisterAttached("ObservableRegionContext", typeof(ObservableObject<object>), typeof(RegionContext), null);

		/// <summary>
		/// Returns an <see cref="ObservableObject{T}"/> wrapper around the RegionContext value. The RegionContext
		/// will be set on any views (dependency objects) that are inside the <see cref="IRegion.Views"/> collection by 
		/// the <see cref="BindRegionContextToDependencyObjectBehavior"/> Behavior.
		/// The RegionContext will also be set to the control that hosts the Region, by the <see cref="SyncRegionContextWithHostBehavior"/> Behavior.
		/// 
		/// If the <see cref="ObservableObject{T}"/> wrapper does not already exist, an empty one will be created. This way, an observer can 
		/// notify when the value is set for the first time. 
		/// </summary>
		/// <param name="view">Any view that hold the RegionContext value. </param>
		/// <returns>Wrapper around the Regioncontext value. </returns>
		public static ObservableObject<object> GetObservableContext(DependencyObject view)
		{
			if (view == null) throw new ArgumentNullException("view");

			ObservableObject<object> context = view.GetValue(ObservableRegionContextProperty) as ObservableObject<object>;

			if (context == null)
			{
				context = new ObservableObject<object>();
				view.SetValue(ObservableRegionContextProperty, context);
			}

			return context;
		}

	}
}